Attention has been focused recently on the hydrolysis of metal alkoxides as new techniques for producing base powder for ceramics. This method makes use of the peculiar property of the metal alkoxides of the formula M(OR).sub.n (wherein M is a metal atom of n valences and R is an alkyl group) that they are reacted with water to produce metal oxides or hydroxides and an alcohol according to the following reaction formula: EQU 2M(OR).sub.n +nH.sub.2 O.fwdarw.2MO.sub.n/2 +2nROH EQU M(OR).sub.n +nH.sub.2 O.fwdarw.M(OH).sub.n +nROH
The powder of TiO.sub.2 or SiO.sub.2 synthesized by this method is particulate, narrow in particle size distribution and also high in purity, so that it has high availability as a powder material for ceramics.
It has been also practiced in the art to synthesize the oxides containing two or more type of metals by the hydrolysis of a mixed solution of two or more types of metal alkoxides. For example, BaTiO.sub.3 having a perovskite structure is synthesized by dissolving barium alkoxide and titanium alkoxide in a 1:1 molar ratio in an organic solvent and adding water dropwise to the mixed solution to effectuate the hydrolysis thereof (see Japanese Patent Kokai (Laid-Open) No. 82119/82). According to the conventional method in which BaCO.sub.3 and TiO.sub.2 are mixed and calcined, a high temperature of around 1,000.degree. C. is required for the synthesis of BaTiO.sub.3, but when said metal alkoxides hydrolysis method is employed, it is unnecessitated to use such a high temperature and crystalline BaTiO.sub.3 can be obtained by controlling the temperature of the solution at 60.degree. to 70.degree. C. Therefore, the products by this hydrolysis method had many advantages over those by the conventional method, such as no fear of contamination by the impurities at the time of mixing of the materials by a ball mill or such and no possibility of suffering from an increase of particle size or a drop of surface activity which could be caused by a high-temperature heat treatment.
As the oxides containing two or more types of metals and synthesizable as a crystalline powder by said hydrolysis method, there are known the perovskite type compounds such as SrTiO.sub.3, Ba(Ti.sub.1-x Zr.sub.x)O.sub.3,, BaZrO.sub.3 and (Ba.sub.1-x Sr.sub.x)TiO.sub.3 and their solid solutions (Japanese Patent Kokai No. 2220/83); ferrite compounds such as MnFe.sub.2 O.sub.4, (Mn.sub.1-x Zn.sub.x)Fe.sub.2 O.sub.4 and NiFe.sub.2 O.sub.4 (Japanese Patent Kokai No. 26726/82); germanates such as SrGeO.sub.3, PbGeO.sub.3 and ZnGeO.sub.4 (Japanese Patent Kokai No. 199717/83); PbWO.sub.4, SrAS.sub.2 O.sub.6, etc.
However, when it is tried to synthesize a complex perovskite type compound having a more complicate structure and represented by the general formula A(B.sub.x, C.sub.y)O.sub.3 (where A, B and C are the metal atoms of p, q and r valences, respectively, and q.noteq.r, x+y+1, and xq+yr=6-p) by using said hydrolysis method, there can be synthesized only the amorphous-state powders when the ordinarily used techniques are employed, and for crystallizing them, heating to a temperature of around 500.degree. to 700.degree. C. is required. Thus, in the synthesis of such compounds by the hydrolysis method using the conventional techniques, efficient use was not made of the merit of this hydrolysis method in being capable of low-temperature synthesis of ultrafine particles.